Take away its success and the glamour will go, leaving only a rump of fanatics

We are not engaged in a religious war. This is not a confrontation between Islam and the West. To start from that premise is to place Isil (which should not be called by its presumptive title “Islamic State”) on precisely the ground it wishes to occupy. As the voices of what the media calls “moderate Muslims” – who should actually just be described as “Muslims” – say repeatedly, the activities of these terrorist criminals hacking their way through northern Iraq have nothing to do with the Islamic faith.

Odd as it may seem at a time of death and destruction, it is important to pay attention to words. To give the combatants the description they seize for themselves is to lose half the moral argument that must be won before effective action can be taken. So it is more important than ever to say that this is not a struggle between “our values” and those of medieval fundamentalism, or Islamist extremism.

The contest is not modern liberal democracy versus the Dark Ages. This is to impose meaning on what is, in truth, meaningless. There is nothing coherent or comprehensible at the heart of the homicidal Isil frenzy. It is just what it looks like: psychopathic nihilism.

Indeed, it may be worse than counterproductive to deal with Isil as if it were a rational force with established roots and a comprehensible set of demands capable of political solution. Just as this is not about religion, it is also not about politics, which only comes into play if there is an agreement at the start that life itself is worth having.

There is not even anything particularly Middle Eastern in the Isil mode of operation. In fact, the gratuitous violence and promiscuous mayhem of its onslaught resembles nothing so much as 19th-century European anarchism, whose objective was simply to create the maximum amount of indiscriminate chaos with the vague intention of undermining the existing order.

Nor are the utterances that the West has come to regard as characteristic of this contemporary terrorist threat uniquely “Islamist”. The infamous taunt of al-Qaeda, which it boasted would always guarantee its victory – “You love life, we love death” – was a widely held sentiment in the anarchist movement.

In Joseph Conrad’s novel The Secret Agent, about London anarchists in the 1890s, a chief instigator and bomb expert derides the enemy in precisely these terms: “They depend on life [which is] open to attack at every point; whereas I depend on death, which knows no restraint and cannot be attacked. My superiority is evident.”

So, no, there is nothing original or unprecedented about this. The world has dealt with mass psychosis before – or rather, failed to deal with it. It would be unforgiveable to make the same fatal mistake again: to treat what is really a form of mindlessness as if it were a rational programme that could somehow be accommodated in the global debate.

“We love death” is not a negotiable demand. Murdering a Western journalist who had been reporting outrages of the kind which Isil itself condemned is not an intelligible move in any campaign that is susceptible to argument. Far from being a homogeneous, principled force, there is no common root of grievance among the Isil ranks: the British Pakistani recruits will be more concerned about Kashmir than Gaza or Iraq.

And some of them seem to have had relatively little understanding of the religious cause to which they were ostensibly committed, like Mohamed Ahmed and Yusuf Sarwar, who ordered Islam for Dummies and The Koran for Dummies from Amazon before they departed for their terrorist sojourn in Syria.

The next obvious question: how do you fight a dream that is without identifiable substance or consistent objectives? If the demands are so wild, so mercurial, so fantastic that there cannot even be a common language for discussing them – what then? First, by recognising it for what it is: this is a fantasy of invincibility. Any possibility of eliminating it as a threat will have to treat it as a delusion which must be undermined, not a lucid plan that can be defeated by diplomatic strategy.

What follows from this is that every withdrawal from confrontation, every backward step – such as Barack Obama’s retreat from his “red line” in Syria – is catastrophic. Each time the West (or the Iraqi government) has a failure of nerve, it reinforces the myth of invulnerability – and another tranche of baby-faced malcontents flies out to sign up for global jihad.

This illusion of world-beating power, there for the taking if you kill everybody in the way, must be extirpated. As the American government seems to be beginning to understand, it can only be broken by unflinching resolve and intimidating force. Barack Obama – the president who never wanted to deal with foreign policy at all, and who appears frighteningly out of his depth – may have to come to terms with the fact that the world cannot just be told to go away and leave the only remaining superpower in peace.

What does this mean in practice? Take away the success and the glamour will go too, until eventually the delusion cannot be maintained except by a rump of fanatics who can be isolated. Make the defeats as ignominious and mortifying, and as visible, as possible. Arm the honourable combatants, such as the Kurds, and intervene on their behalf when necessary.

Above all, avoid any alliance of convenience with a regime such as Assad’s in Syria, whose criminal attacks on its own population helped to create the Isil phenomenon. Even if such an arrangement were to bring temporary relief, a victory on such terms would inevitably spawn another terrorist incarnation: Isil under a new name would be up and running again within a year.

François Hollande is (unusually) right to say that, if one year ago we had reacted to the use of chemical weapons in Syria “we wouldn’t have had this terrible choice between a dictator and a terrorist group”. But we are where we are. The consequences of last year’s cowardice must be a lesson learnt. Philip Hammond, the Foreign Secretary, has, thank goodness, ruled out any such rapprochement with Assad, but keep an eye on Washington, which may be in the market for easy (or easier) answers.

Even now, the Obama administration is talking about “smart power” as an alternative to “boots on the ground”. What is the force of this distinction? There is only one kind of power that can demoralise and eventually destroy a movement that is beyond reason. This may come as a shock to a White House that seems to have so much faith in the magical power of language, but if military intervention is categorically ruled out, then no amount of smart talk will be any use.